1. Field of the Invention
This invention relates generally to the field of general purpose microcomputers and particularly to a microcomputer unit including a serial interface controller such as the Universal Serial Bus (USB) RAM device to facilitate communication between a host and a microcontroller.
2. Description of the Prior Art
The growth of desktop computers has been accompanied by a corresponding growth in the number and types of peripheral devices that have various connection/interconnection schemes, etc. Accordingly, today's PC's have many peripheral connectors, most of which are expensive. As the size and cost of the PC decreases, the relative cost of these connectors increase. To alleviate this problem, high performance serial bus schemes are being defined that are designed to use one connector to attach many (lower performance) peripherals to the PC. Furthermore, due to the operational limitations of many of these peripheral devices with respect to what is referred to in the computer industry as "low speed", they typically require dedicated wires and connectors capable of supporting much higher speed data transfers than are required.
Moreover, information flows and the required responses over a high performance serial bus exceed the performance capability of generic microcontrollers of the type used in typical peripherals.
The Universal Serial Bus (USB) and "firewire" (IEEE 1394) has been introduced in the computer industry to effectuate "time sharing" of many of these low speed peripheral devices over a single higher speed connection thereby providing higher performance communication links while using such peripheral devices. This higher speed connection requires only minimal resources (such as I/O, DMA, Interrupt and Memory) from the host system. Prior art systems require such resources per peripheral.
By way of background, a summary of the USB and its operation is presented below. Although the preferred implementation of the serial interface bus is the USB, a similar approach will work with the faster "firewire" (IEEE 1394) operating at 100,200,400 . . . Mbits/sec.